1. Field of the Invention
The present invention relates to a color cathode ray tube and an electron gun, and more particularly, to a color cathode ray tube and an electron gun in which the deflection aberration is efficiently improved by using a magnetic material formed at the electron gun, and the resolution of a display screen is also improved.
2. Description of the Related Art
FIG. 1 illustrates the configuration of a color cathode ray tube according to the related art.
Referring to FIG. 1, the color cathode ray tube of the related art is a kind of vacuum tube that includes a panel 1 placed at a front glass and a funnel 2, which is a rear glass, sealed and coupled with the panel 1 so that the flat color cathode ray tube has a vacuum inside.
Red, blue and green (R, G and B) fluorescent materials are coated on an inner surface of the panel 1 to form a fluorescent screen 11. An electron gun 8 is installed at a neck portion of the funnel 2 opposite to the fluorescent screen 11.
A shadow mask 3 to select colors is installed between the fluorescent screen 11 and the electron gun 8, and spaced by a predetermined distance from the fluorescent screen 11. The shadow mask 3 is coupled with a mask frame 4, elastically supported by a spring 5, and supported on the panel 1 by a stud pin 6. In addition, the mask frame 4 is coupled with a magnetic inner shield 7 to reduce the effect of the earth magnetic field at the rear of the cathode ray tube to reduce the movement of electron beam 6 caused by external magnetic field.
Meanwhile, a convergence purity correction magnet (CPM) 10 is installed at a neck portion of the funnel 2 to control an RGB electron beam so that the electron beam is converged on one spot. In addition, a reinforcement band 12 is installed to strengthen the front glass against the internal vacuum.
The operation of the color cathode ray tube configured as described above will be described. The electron beam emitted from the electron gun 8 is deflected in vertical and horizontal directions by the deflection yoke 9. The deflected electron beam passes a beam passage hole of the shadow mask 3 and collides with the front fluorescent screen 11 to display a desired color image. Here, a convergence purity correction magnet 10 corrects the convergence and purity of the R, G and B electron beams, and an inner shield 7 shields the electron beams from the effects of the earth magnetic field at the rear of a cathode ray tube.
FIG. 2 illustrates the configuration of an electron gun according to the related art. An electron gun 8 includes three cathodes 80 independent from each other, a first electrode (GI) 81 installed separated from the cathode 80 at a predetermined distance, a second electrode (G2) 82 spaced from the first electrode (G1) 81 at a predetermined distance, a third electrode (G3) 83 spaced from the second electrode (G2) 82 with a predetermined distance, a fourth electrode (G4) 84 spaced from the third electrode (G3) 83 at a predetermined distance, a fifth electrode (G5) 85 spaced from the fourth electrode (G4) 84 at a predetermined distance, a sixth electrode (G6) 86 spaced from the fifth electrode (G5) 85 at a predetermined distance, and shield cup 87.
The deflection yoke 9 that deflects an electron beam across the entire screen is installed at an outer side of the neck portion of the funnel 2 having an electron gun 8. Here, a ground voltage is applied to the first electrode 81. A static voltage of about 600 V is applied to the second electrode 82 and the fourth electrode 84. A dynamic focus voltage is applied to the third electrode 83 and the fifth electrode 85. A static voltage of about 26000 V is applied to the sixth electrode 86.
Operation of an electron beam will be described referring to the configuration described above. The amount of hot electrons emitted from a hot heater is controlled by the first electrode 81 and the hot electrons are accelerated by the second electrode 82. The hot electrons pass through the third electrode 83, the fourth electrode 84, the fifth electrode 85 and the sixth electrode 86 in series that are converging electrodes so that the hot electrons are converged and accelerated finally to collide with the screen.
These R, G and B electron beams converge on the center of the screen by a static convergence operation of a main lens. If three electron beams are deflected away from the center of the screen using a uniform magnetic field, the three electron beams focus before they reach the screen and they deviate with each other because of the distance between the electron guns and the screen.
To overcome this problem without any additional circuitry, a self-convergence magnetic field is used. The self-convergence magnetic field is formed to be a pincushion type field horizontally and to be barrel type field vertically.
FIG. 3 illustrates a self-convergence magnetic field. The R, G and B electron beams arranged inline are converged on the screen without any additional dynamic convergence because a self-convergence magnetic field consists of a pincushion type horizontal deflection magnetic field (HB) and a barrel type vertical deflection magnetic field (VB).
However, as shown in FIG. 4, the cross-sections of R and B electron beams positioned at the ends of three electron beams arranged inline are distorted because the density of the magnetic field formed by the deflection yoke gets dense as it travels from the center portion to the peripheral portion. Accordingly, to improve the focus at the periphery of the screen, a dynamic focus voltage should be applied to each of electron beams, but the focus of the R and B electron beams deteriorates because the same dynamic focus voltage is applied to the three electron beams in an inline electron gun in which a passage hole for R, G and B three electron beams is formed from one electrode.
FIG. 5 illustrates a pincushion type horizontal deflection magnetic field. The three electron beams are deflected by a pincushion type horizontal deflection magnetic field (HB) as shown in FIG. 5 that forms a self-convergence magnetic field along with a barrel type vertical deflection magnetic field (VB) to converge to one point.
However, the electron beams are distorted by self-convergence magnetic field. Especially, the R, G and B electron beams are affected by focusing forces in different vertical directions at the left and right sides of the screen. Accordingly, on the right side of the screen, a haze in which the red electron beam gets blurry is caused, and a haze of the blue beam is caused on the left side of the screen so that the resolution degenerates on the entire screen.
FIG. 6 illustrates the pincushion magnetic field caused by a deflection yoke in a shield cup of an electron gun and the force applied to the electron beam. For example, supposing that the electron beam is emitted forward out of the figure towards the reader, if the magnetic field is directed upwards, the three electron beams are affected by the force in a direction to the right. However, as shown in FIG. 6, the red electron beam is affected by the divergent force in a direction orthogonal to the magnetic field and the blue electron beam is affected by the convergent force in a direction orthogonal to the magnetic field according to the form of the pin-cushion type horizontal deflection magnetic field so that a blooming phenomenon is caused by the red electron beam and a halo phenomenon is caused by the blue electron beam on the left side of the screen. In contrast, a halo phenomenon is caused by the red electron beam and a blooming phenomenon is caused by the blue electron beam on the right side of the screen.
FIGS. 7a, 7b, and 7c illustrate that the cross-sections of the R and B electron beams on both edges of R, G and B electron beams arranged inline are distorted.
FIG. 7a illustrates a pincushion type magnetic field of a deflection yoke when the electron beams are deflected to the left side of the screen. FIG. 7b illustrates that the B beam causes a halo phenomenon when deflected to the left of the screen. FIG. 7c illustrates that the R beam causes a blooming phenomenon when deflected to the left of the screen. In other words, as shown in FIG. 7a, the R and B electron beams undergo a force in the direction of the arrow mark on the drawing because of the pin-cushion type magnetic field of the deflection yoke. The B electron beam undergoes a force of the converging magnetic field and the R electron beam undergo a force of the diverging magnetic field.
As a result, when deflected in the left direction, the R electron beam causes a blooming phenomenon since lenses are formed as shown in FIG. 7b and the B electron beam causes a halo phenomenon since lenses are formed as shown in FIG. 7c. In contrast, the phenomena are switched when the electron beams are deflected in the right direction.
The halo phenomenon and the blooming phenomenon for the R and B electron beams increase and the size of the electron beams on the fluorescent screen vary as they scan to the periphery of the screen. This non-uniform cross-section of the electron beam deteriorates resolution of image. An electron gun that reduces coma aberration has been suggested to solve this problem.
For example, Japan Open Laid Application No. 10-116570 discloses that the deflection aberration is corrected using a magnetic piece for a portion of an electrode of the electron gun and using a separate magnetic field generating means synchronized with the deflection signal. However, this solution is more expensive, and it is difficult to manufacture because a separate magnetic field generating means is installed on the outer portion of the neck and a signal synchronized with deflection is applied to the magnetic field generating means while a magnetic piece is installed in the electron gun. Because the separate magnetic field generating means installed on the outer portion of the neck is synchronized with the deflection of the deflection yoke and is coupled with the deflection yoke, the deflection sensitivity of the deflection yoke is decreased so that power consumption is increased and additional heat is generated. So, this solution is difficult to apply.
Korean Laid-Open Patent Publication No. 2001-0091314 discloses that a deflection aberration is improved using a magnetic field created by a magnetic piece installed at the electron gun and the deflection yoke so that it is easy to apply the magnetic field. However, leakage magnetic field is not used enough since a small magnetic piece is disposed between an outer beam passage hole and a center passage hole.
In addition, another method has been studied in which an astigmatism lens is installed in the area of the electrode that constitutes a provisional converging lens to form a uniform electron beam cross-section across the entire fluorescent screen. The aspects of the first electrode of the electron beam and the electron beam passage hole of the second electrode are formed to be different from each other to prevent the electron beam which lands on the center and the periphery of the fluorescent screen from being distorted. However, it is very difficult to manufacture and control this astigmatism lens.